must yawn
Regular verb: yawn - yawned- yawned

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must yawn
you must yawn
she must yawn
we must yawn
you must yawn
they must yawn 	I must be yawning
you must be yawning
she must be yawning
we must be yawning
you must be yawning
they must be yawning	I must have yawned
you must have yawned
she must have yawned
we must have yawned
you must have yawned
they must have yawned	I must have been yawning
you must have been yawning
she must have been yawning
we must have been yawning
you must have been yawning
they must have been yawning	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must not yawn
you must not yawn
she must not yawn
we must not yawn
you must not yawn
they must not yawn 	I must not be yawning
you must not be yawning
she must not be yawning
we must not be yawning
you must not be yawning
they must not be yawning	I must not have yawned
you must not have yawned
she must not have yawned
we must not have yawned
you must not have yawned
they must not have yawned	I must not have been yawning
you must not have been yawning
she must not have been yawning
we must not have been yawning
you must not have been yawning
they must not have been yawning	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I yawn?
must you yawn?
must she yawn?
must we yawn?
must you yawn?
must they yawn? 	must I be yawning?
must you be yawning?
must she be yawning?
must we be yawning?
must you be yawning?
must they be yawning? 	must I have yawned?
must you have yawned?
must she have yawned?
must we have yawned?
must you have yawned?
must they have yawned? 	must I have been yawning?
must you have been yawning?
must she have been yawning?
must we have been yawning?
must you have been yawning?
must they have been yawning? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I not yawn?
must you not yawn?
must she not yawn?
must we not yawn?
must you not yawn?
must they not yawn? 	must I not be yawning?
must you not be yawning?
must she not be yawning?
must we not be yawning?
must you not be yawning?
must they not be yawning? 	must I not have yawned?
must you not have yawned?
must she not have yawned?
must we not have yawned?
must you not have yawned?
must they not have yawned? 	must I not have been yawning?
must you not have been yawning?
must she not have been yawning?
must we not have been yawning?
must you not have been yawning?
must they not have been yawning?